There was a car in front of me that was making weird movements, so it was scary.
The car that was running before mine was moving about in a strange way, so I was scared.
ご質問ありがとうございます。
① "There was a car in front of me that was making weird movements,"＝「私の前にいた車は変な動作をしていた、」
"so it was scary."＝「なので怖かった。」
② "The car that was running before mine was moving about in a strange way,"＝「私の前に走っている車は変な動きをしていた、」
"so I was scared."＝「なので、私は怖かった。」
ご参考までに。
アメリカ合衆国 
